Aspects of a method for 3D finite element computation of unsteady, 
incompressible free-surface flow are presented. The approach is based on the 
Deformable-Spatial-Domain/ Stabilized Space-Time (DSD/SST) finite element 
formulation, which takes automatically into account the deformation of
the elements in response to the motion of the free surface. The 
free-surface elevation is governed by a kinematic free-surface 
condition, which is also solved with a stabilized formulation. 
A new governing equation and stabilized formulation is derived
for cases where the channel walls are not vertical.
The parallel implementation based on MPI message-passing standard
is fully portable, and have been demonstrated to be scalable on a
range of architectures. A 3D computation of a flow past a spillway
of a dam is shown as an example application.